There are terminal devices, such as personal computers, tablet-type mobile terminals, or the like, and servers that recognize face information obtained from input images by cameras, that check the recognized face information against face information on a subject person that is previously stored in the terminal device or the server, and that perform recognition on the subject person (hereinafter, referred to as face recognition). The terminal devices or the servers perform, by recognizing the subject person from the face recognition, login authentication of the terminal devices or permission to use services through Web browsers or the like using the servers.
The face recognition specifies the distinctive portion, such as the eye, the nose, the mouth, a mole (lentigo), or the like, of the face on the input image (hereinafter, referred to as a feature point); judges the position of the portion with respect to the subject feature point or the distance between the feature points (hereinafter, referred to as the distance between the feature points), the position, the size, or the color of each of the portions with respect to the face; and checks the judged portion against the previously stored face information on the subject person.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-219899
Patent Document 2: Japanese Laid-open Patent Publication No. 2013-117794
By the way, in front of the camera, the face is not always facing the front and the face may sometimes faces sideways or upward. Thus, the orientation of the face on an input image is not always the same. Consequently, when periodically checking, by using the face recognition, a person who uses a terminal device or a server after the login authentication has been performed or a user of the service after the use permission has been given, there is a need to perform the face recognition based on the face not only the face facing to the front but also the face facing upward, downward, to the left, or to the right.
However, in the technology described above, if the orientation of the face of the subject person previously stored in the face information is different from the orientation of the face of the input image, because the position of the feature point and the distance between the feature points greatly vary depending on the orientation of the face, there is sometimes a case of not recognizing the subject person. For example, if the orientation of the face of the subject person previously stored in the face information is the orientation facing the front, it is not possible to accurately perform the face recognition based on the face facing upward, downward, to the left, or to the right.
Accordingly, it is an object in one aspect of an embodiment of the invention to provide face recognition even if a face is inclined.